The present invention relates to a multistage gas generator for an air bag and an air bag apparatus using the gas generator.
An air bag system which is mounted on various kinds of vehicles and the like including automobiles, aims to hold an occupant by means of an air bag (a bag body) rapidly inflated by a gas when the vehicle collides at a high speed so as to prevent the occupant from crashing into a hard portion inside the vehicle such as a steering wheel, a windscreen due to an inertia and being injured. This kind of air bag system generally comprises a gas generator to be actuated according to a collision of the vehicle and discharge a gas, and an air bag to introduce the gas to inflate.
It is desired that the air bag system of this type can safely restrain the occupant even when frame of the occupant (for example, whether a sitting height is long or short, whether an adult or a child, and the like), a sitting attitude (for example, an attitude of holding on the steering wheel) and the like are different. Then, there has been conventionally suggested an air bag system which actuates, applying an impact to the occupant as small as possible at the initial stage of the actuation. Gas generators in such a system are disclosed in JP-A 8-207696, U.S. Pat. Nos. 4,998,751 and 4,950,458. JP-A 8-207696 suggests a gas generator in which one igniter ignites two kinds of gas generating agent capsules so as to generate the gas at two stages. U.S. Pat. Nos. 4,998,751 and 4,950,458 suggest a gas generator in which two combustion chambers are provided for controlling actuation of the gas generator so as to generate the gas at two stages due to a expanded flame of the gas generating agent.
Further, in JP-A 9-183359, and DE-B 19620758, there is disclosed a gas generator in which two combustion chambers storing a gas generating agent are provided in a housing and an igniter is arranged in each combustion chamber, so as to adjust an activation timing of each of the igniters, thereby adjusting an output of the gas generator.
However, these above conventional gas generators are not a multistage gas generator for an air bag with a simple structure which can be manufactured easily, suppressing the entire size of the container (housing).
The present invention provides a multistage gas generator for an air bag, wherein, at the initial stage of actuation, the gas generator is actuated to give a passenger as a small impact as possible, and according to variation of passengers"" physiques (such that a sitting height is tall or low, adult or child) and sitting postures (such as clinging to a steering wheel), actuation output of the gas generator and timing of increase of output can be arbitrarily adjusted in order to restrain the passenger safely, and the gas generator can be manufactured easily with a simple structure, the entire size of the container (housing) can be suppressed, and finally the volume ratio of each combustion chamber can be arbitrarily be adjusted.
The present invention is characterized in an inner structure, specially a layout structure of the combustion chambers capable of suppressing the entire size of the gas generator and adjusting the volume ratio of each of the combustion chambers arbitrarily in a multistage gas generator for an air bag provided with a plural combustion chambers inside the housing thereof.
In other words, the multistage gas generator of the present invention having a cylindrical housing comprising a diffuser shell with a plurality of gas discharge ports formed in a cylindrical side wall and a closure shell forming a inner space with the diffuser shell, a plurality of combustion chambers for accommodating gas generating means provided in a cylindrical housing, and ignition means disposed in the respective combustion chambers to ignite and burn the gas generating means, wherein, in the housing, at least one of the combustion chambers is disposed in the inner side of an inner shell provided eccentrically with respect to a center axis of the housing, the ignition means provided for the respective combustion chambers are disposed eccentrically with respect to the center axis of the housing.
Further, in the gas generator of the present invention, a communication hole which allows mutual communication between the combustion chambers can be provided.
An automatic ignition material (AIM) which is to be ignited and burnt by transmitted heat may be disposed in either one of the combustion chambers.
The present invention further provides a multistage air bag apparatus which comprises the above-described gas generator, an ignition signal-outputting means provided with as many outputting portions, which outputs activation signals to the igniters on impact, as the igniters of the ignition means, and a plurality of lead wires having connectors, the igniters and the outputting portions are connected to each other through the lead wires having the connectors, and the connectors include defining means for deciding the unique connection between one of the connectors and one of the outputting portions.
The above gas generator may further comprise a cylindrical filter means for purifying and/or cooling an activation gas, one or both of axial end surfaces of the filter means may be formed as inclining end surfaces which get narrower in the axial extending direction and the interior angle with respect to the inner peripheral surface is an acute angle, and a supporting portion which is opposed to the inclining end surface of the filter may be provided in the housing (a self-contracting type filter).
In the present invention, most of an outer surface of the inner shell can be in direct contact with gas generating agent existing outside of the inner shell without interposing a heat insulator. The gas generating agent comes into contact with the outer surface of the inner shell where the communication hole is provided. A wall of the inner shell exists between a first gas generating agent which burns first and the other second gas generating agent. Even if the first gas generating burns, the second gas generating agent will never start burning before actuation of a second igniter, and the second gas generating agent is burnt by actuation of the second igniter before a temperature of the second gas generating agent reaches an ignition temperature by heat transfer.
After the first gas generating is ignited, if the gas generator is left standing without igniting the second gas generating agent, the second gas generating agent is ignited after about 10 seconds.
In the present invention, it is generally preferable that the inner shell is of cylindrical shape whose upper end is closed and its horizontal cross sectional shape is circular. The horizontal cross sectional shape of the inner shell may be formed into various shapes such as rectangular shape and elliptic shape. However, it is desirable to form the horizontal cross sectional shape of the inner shell into circular in view of easiness of connection. The inner shell is disposed in the housing eccentrically with respect to the center axis of the housing. That is, the inner shell is disposed in the housing such that a center of the inner shell does not coincide with a center of the housing, and the inner shell is disposed in the housing eccentrically with respect to the cylindrical housing. Therefore, even if the plane shape of the housing is substantially elliptic, in case that the center of the plane shape and the center of the inner shell are deviated from each other, the inner shell and the housing are deviated from each other. Besides, the center axis of the housing is specified exclusively based on the plane shape of the cylindrical body, and even if the housing has a flange for mounting the housing to the module, the flange is not taken into consideration when the center axis of the housing is specified.
The ignition means disposed in the respective combustion chambers include an igniter which is actuated by electric signal. The igniters can be provided aligned in the axial direction of the housing. The closure shell constituting the housing can include a collar portion for fixing the igniter, and the igniter can be fixed to the collar portion. In this case, it is preferable that all igniters included in the respective ignition means are fixed to a single collar portion. This is because when the closure shell is formed including the collar portion, by fixing the plurality of igniters to the collar portion beforehand, the plurality of igniters can be fixed in the housing with a single operation for forming the closure shell, which is advantageous in manufacture.
The inner shell disposed in the housing eccentrically is of cylindrical shape and the inner shell includes an opening portion which opens by combustion of the gas generating means in one of the combustion chambers. The inner shell can be formed into another shape as described above. However, in view of easiness in connecting to the closure shell, it is preferable that the plane cross sectional shape is circle. The inner shell enable the gas to flow through the combustion chambers which are defined inside and outside of the inner shell by opening the opening portion. Such opening portion may be formed by forming a plurality of holes in the peripheral wall of the inner shell, and by closing the holes using breaking members. The holes closed by the breaking members can be opened exclusively by burning the gas generating means in the combustion chambers provided inside the inner shell. The hole is opened by combustion of the gas generating means, e.g., by rupturing, peeling, burning or detaching the breaking member due to a pressure caused by combustion of the gas generating means. Alternatively, this can be realized by providing the inner shell with a notch or by reducing the thickness of a portion of the inner shell. A shielding plate can be disposed outside of the opening portion, and the shielding plate can prevent flame generated in the combustion chamber provided outside the inner shell from coming into direct contact with the opening portion. The opening portion may be formed such as to be opened only by combustion of the gas generating means in one of the combustion chambers.
As described above, the inner shell is disposed in the housing eccentrically with respect to the center axis of the housing, and the ignition means disposed in each of the combustion chambers is disposed eccentrically with respect to the center axis of the housing. With this structure, it is possible to suppress the size of the housing to the minimum, and flexibility in volume, layout and the like of the combustion chamber can be maximized. That is, when two combustion chambers are defined in the housing, by disposing the inner shell eccentrically in the housing and defining a first combustion chamber on the outer side thereof and defining a second combustion chamber on the inner side, the volume ratio of the first and second combustion chambers can be freely changed by changing the volume of the inner shell. At that time, if the igniter of the ignition means disposed in each of the combustion chambers is also disposed eccentrically with respect to the center axis of the housing, the igniter disposed in the first combustion chamber will not be an obstacle to increase the volume of the second combustion chamber. Therefore, in the present invention, it is possible to maximize the flexibility in volume and the like of the first and second combustion chambers.
Further, the present invention provides a multistage gas generator for an air bag which is provided, in the combustion chamber inside the inner shell, with an automatic ignition material (AIM), to be ignited and burnt by heat generated by combustion of the gas generating means disposed in the combustion chamber outside the inner shell, and also provides a multistage gas generator for an air bag in which the automatic ignition material (AIM) is included in the ignition means disposed in the combustion chamber inside the inner shell. That is, in most cases, when the multistage type gas generator is actuated, all the ignition means are actuated and the gas generating means in all the combustion chambers are burnt. However, under a certain actuating condition, there is a case in which only one of the ignition means is actuated intentionally to burn the gas generating means in a selected combustion chamber. In this case, remaining ignition means and gas generating means which were not actuated cause inconvenience at the time of later disposal or damping. Therefore, it is preferable to ignite and burn them after actuation of the gas generator. Thereupon, by disposing the automatic ignition material (AIM) in the combustion chamber and/or ignition means, even when the gas generating means and/or ignition means in either of the combustion chambers were not burnt and remained, it is possible to ignite and burn the gas generating and/or ignition means at a delayed timing by heat (transmitted heat) caused by combustion of the gas generating means in the other combustion chamber. Therefore, in the present invention also, in the combustion chamber and/or the ignition means provided inside the inner shell, it is preferable to dispose the automatic ignition material (AIM) which is to be ignited and burnt by heat generated by combustion of the gas generating means in the combustion chamber provided outside the inner shell. As the automatic ignition material (AIM), material which is ignited with a lower temperature compared with the gas generating means or transfer charge is preferably used. The gas generating means is ignited by the automatic ignition material (AIM) after activation of the gas generating means. That is, the ignition of the gas generating means by the automatic ignition material is different from the ignition of the gas generating agent delaying intentionally the actuation timing of the ignition means for the purpose of adjusting the actuation performance of the gas generator. The ignition by AIM is performed when a sufficient period of time has passed after actuations at intentional intervals of the igniters to adjust the actuation performance of the gas generator. Therefore, after one ignition means is actuated first, the remaining gas generating means will not be ignited by the automatic ignition material before the other ignition means is actuated with intentionally delayed timing.
The housing can be formed by joining the diffuser shell and the closure shell by various welding methods such as friction welding, electron beam welding, laser welding, TIG welding and projection welding. Among these welding methods, when both the shells are joined by friction welding to form the housing, it is preferable to carry out the friction welding while fixing the closure shell. Generally, both the shells are joined at the final stage. And by performing the friction welding while fixing the closure shell in this manner, even when the center of gravity of the closure shell side is deviated such that the ignition means is disposed eccentrically, both the shells can be stably be joined. In other words, the friction welding is carried out in a state where one object is fixed and the other object is rotated. If the center of gravity of the object to be rotated is deviated, it is difficult to stably carry out the friction welding. Thereupon, in the present invention, stable friction welding is realized by carrying out the friction welding while fixing the closure shell side.
When the friction welding is carried out while fixing the closure shell, it is preferable that the flange portion for mounting the gas generator to the module case is provided on the closure shell, and the flange portion is formed with a positioning portion for specifying a direction and/or a position of the closure shell which is fixed at the time of friction welding. When the flange portion has a plurality radially projections for fixing the gas generator to the module case, the positioning portion is realized by forming the projections asymmetrically with respect to each other. Only one projecting is provided, the projection itself can be the positioning portion. By forming the flange portion with the positioning portion in this manner, when the inner shell is fixed in the housing by the friction welding, the joining position of the housing is always determined constantly with respect to the inner shell which is rotated. Therefore, it is possible to reliably fix the inner shell in a predetermined direction and/or position. By forming the positioning portion on the flange portion, the flange portion is used both for positioning and mounting of the gas generator. In the present invention, in order to fix the closure shell in the predetermined direction and/or a position at the time of friction welding, it is of course possible to form the positioning portion on another portion such as a peripheral wall and bottom surface instead of the flange.
Further, the igniting means disposed in the combustion chamber can include injecting-direction restricting means for restricting an injecting direction of flame which is generated by the actuation of the ignition means. The injecting-direction restricting means is used for restricting the injecting direction of flame generated by actuation of the ignition means, i.e., the injecting direction of flame to ignite and burn the gas generating means.
The injecting-direction restricting means can envelop at least a portion of the ignition means which generates the flame, and includes a hollow container having two or more flame-transferring holes for restricting the injecting direction of the flame into a desired direction. Examples of such injecting-direction restricting means are deflector plates, a cylindrical member capable of enveloping the entire ignition means, and a cup-like container or the like capable of enveloping a portion of the ignition means where the flame is generated.
By using such injecting-direction restricting means, it is possible to restrict the injecting direction of flame of the ignition means to a direction along the inner wall surface of the combustion chamber. The xe2x80x9cdirection along the inner wall surface of the combustion chamberxe2x80x9d means that the flame is ejected, moving in a direction which coincides with a shape of the inner wall surface. By restricting the injecting direction of the flame of the ignition means in this manner, it is possible to preferably burn the gas generating means in the combustion chamber even when the ignition means is not disposed at center of the combustion chamber or when the combustion chamber is not circular in shape and a distance between the gas generating means and the ignition means disposed at corners of the combustion chamber is remarkably fair.
As the injecting-direction restricting means, the gas discharge ports may be distributed so that the number of the gas discharge ports formed further from the first igniter may be greater or the total opening area thereof may be greater than otherwise. It is preferable to combine these to form the injecting-direction restricting means.
The outputs of the ignition means disposed in the respective combustion chambers can be changed from one another. When the ignition means include a transfer charge in addition to the igniters having different outputs, it is possible to adjust the material, shape or amount of the transfer charge, thereby adjusting the output of the ignition means.
A retainer can be disposed inside the inner shell in order to perform the connection with the closure shell stably and smoothly. The retainer may be a gas generating agent fixing member shown in the embodiment. When fixing the inner shell to the closure shell by friction welding, crimping, resistance welding, convex-concave joint or the like, the retainer keeps the gas generating agent in the inner shell so that the gas generating agent does not come into direct contact with the closure shell, and also obtains a space for accommodating the ignition means in the inner shell. By using this retainer, the assembling operation can be facilitated. Especially when charging directions of two or more gas generating means are different at the time of assembling as in the present invention, it is effective to use the retainer. The retainer may have a canister-like shape made of aluminum or iron, or may be a porous material made of wire mesh or the like.
The igniter included in the ignition means is activated upon reception of activation signal of the gas generator which is outputted from a control unit or the like. Therefore, a cable for transmitting the activation signal from the control unit or the like is connected to each of the igniters. Since the gas generator of the present invention includes two or more ignition means, two or more igniters are included. By pulling out the cables connected to the igniters in the same direction, the gas generator can be mounted to the module easily afterwards.
In the multistage gas generator for the air bag of the present invention, when the ignition means disposed in each of the combustion chambers comprises an igniter which is to be activated by an electric signal and a cable for transmitting the electric signal is connected to each igniter through a connector, it is preferable that the connector has a positioning means capable of connecting the cable to only one of the igniters. That is, in the cables which are connected to the respective igniters to transmit different activation signals with the aim of adjusting activation timing, if a wrong cable is connected to one of the igniters, a desired activation output can never be obtained. Thereupon, the respective igniters are provided with the respective positioning means to be connected to exclusively one of the cables, which can prevent the connection error. Such positioning means can be realized by forming the engaging portions, which is between the igniter and the connector and for connecting the igniter and the cable, into different shapes for the respective igniters, or by forming the connectors with groove and/or projections having different positions and/or shapes. Additionally, plural cables of the respective igniters can be collected to one connector and the connector can be formed with the positioning means. The positioning means provided in the connector of the invention also includes all cases in which any elements determining whether a plug and a jack can be connected such as a case in which shape and size of a portion (blade or current-carrying plug) which connects and energize the connector) or shape and size of the case of the connector are different. That is, any means which uniquely defines combination of connection between the cable and the ignition is included.
With a gas generator comprising a housing having a plurality of combustion chambers therein and gas generating means which are different from each other in an amount of a generated gas per unit time in the respective combustion chambers such as gas generating means which are different from each other in at least one of burning rate, composition, composition ratio, shape and amount, activation performance of the gas generator, particularly the change with time of the gas discharging amount can be adjusted distinctively and arbitrarily. When the gas generating means in each of the combustion chambers is independently ignited and burnt with arbitrary timing, ignition means which is independently ignited and burnt is disposed in each of the combustion chambers. As the gas generating means, it is possible to use inorganic azide which is conventionally and widely used such as azide-based gas generating agent based on sodium azide or non-azide-based gas generating agent not based on inorganic azide. If safety is taken into consideration, non-azide-based gas generating agent is desirable. The gas generating means is appropriately selected in accordance with requirements such as burning rate, non-toxicity, combustion temperature, decomposition-starting temperature. When gas generating means having different burning rate for each combustion chamber, it is possible to use gas generating means having different composition or composition ratio itself by using inorganic non-azide such as sodium azide, non-azide such as nitroguanidine or the like as fuel and nitrogen source, or gas generating means in which the shape of composition can be changed such as pellet-like, wafer-like, hollow columnar, disk-like, body having a single hole, porous body or the surface area is changed by size of the molded article. Especially when the gas generating means is formed into a porous body having a plurality of through-holes, although layout of the holes is not limited, it is preferable to a distance between an outer end of the molded article and a center of the hole and a distance between the centers of the respective holes are substantially equal to each other so that performance of the gas generator is stabilized. More specifically, in a cylindrical molded article whose cross section is circular, a preferred structure is such that one hole is arranged at the center and six holes are formed around the hole so that the center of each hole is the apex of regular triangles of the equal distances between the holes. Further, it is conceived to dispose one hole at a center and 18 holes around the central hole. The number of holes and layout of the holes are determined based on combination of easiness of manufacture of the gas generating agent, manufacturing cost and performance, and accordingly, the number of holes and layout of the holes are not limited.
In a gas generator (pyrotechnic gas generator) using solid gas generating means for obtaining gas for expanding the air bag, a filter or a coolant is usually preferably used for purifying or cooling combustion gas generated by combustion of the gas generating means. Therefore, in the gas generator of the present invention, when a combustion gas generated by combustion of the gas generating means is purified and/or cooled, filter means formed by compressing laminated wire mesh can be used. If such filter means is formed into self-contracting structure in which the filter means can be pushed radially outward by the pressure of the combustion gas and its upper and lower ends are pressed by the inner surface of the housing, a short pass of the combustion gas between the end surface of the filter means and the inner surface of the housing can be avoided without providing any special member. Such a self-contracting structure can be realized by inclining upper and lower inner surfaces of the housing such as to narrow the inner surfaces, and by inclining upper and lower end surfaces of the filter means such as to be aligned with the upper and lower inner surfaces of the housing. Inside and outside of the filter means can be formed into different laminated wire mesh bodies to provide a triple structure, so that the inner side of the filter means can exhibit protection function of the filter means and the outer side of the filter can exhibit suppressing expansion function of the filter means. The suppressing expansion function can be exhibited by supporting an outer periphery of the filter means with an outer layer made of laminated wire mesh body, porous cylindrical body, annular belt body or the like such as to suppress the expansion.
When the plurality of combustion chambers are provided in the housing and combustion gas is generated by combustion of the gas generating means in the respective combustion chambers as described above, it is preferable that the combustion gas discharged from each combustion chamber passes through a common filter. If all combustion gas passes through the common filter means, it is enough to dispose one filter means in the housing and as a result, the entire volume can be reduced, and the manufacturing cost can be reduced. Further, the combustion gas passing through the common filter means can be discharged from a common gas discharge port(s) formed in the housing.
The above-described gas generator for the air bag is accommodated in a module case together with an air bag (bag) into which gas generated by the gas generator is introduced for expansion, thereby constituting the air bag apparatus. In this air bag apparatus, the gas generator is actuated when an impact sensor senses an impact, thereby discharging the combustion gas from the gas discharge port of the housing. The combustion gas flows into the air bag so that the air bag breaks a module cover and expands, thereby forming a cushion between a passenger and a hard structural member of the vehicle for absorbing the impact.
According to the present invention, there is provided a multistage gas generator for an air bag in which the entire size of the container can be suppressed, the structure is simple and the gas generator can be manufactured easily, the gas generator is actuated, at the initial stage of actuation, to give a passenger as a small impact as possible, and, according to variation of passengers"" physiques (such that a sitting height is tall or low, adult or child) and sitting postures (such as clinging to a steering wheel), actuation output of the gas generator and timing of increase of output can be arbitrarily adjusted in order to restrain the passenger safely.
Further in the gas generator of the invention, at least one of the combustion chambers is disposed eccentrically with respect to the housing, the ignition means provided for each of the combustion chambers is disposed in the housing eccentrically with respect to the housing. With this feature, it is possible to maximize the flexibility of the combustion chamber while suppressing the size of the housing in its radial direction.
The gas generator of the eccentric structure can be realized by including AIM, a connector, a self-contracting type filer which will be explained later, or combination thereof. The gas generator can also be realized by combining other parts described in the present specification.
According to the present invention, the gas generator for the air bag includes a plurality of igniters, activation signals are outputted from the ignition signal-outputting means to the igniters respectively, connection error between each igniter and the ignition signal outputting apparatus outputting section is eliminated, and the multistage type gas generator can always actuate with desired output. Therefore, in the multistage type air bag apparatus capable of adjusting actuation output and timing of output increase, desired actuation performance can always be obtained.
Further, also when the filter means radially expands by passage of the activation gas, since the inclining end surface of the filter means is in contact with the supporting portion in the housing and the surface contact between both the members can be maintained, and thereby, short pass of the activation gas can be effectively avoided. Since the filter means is a member capable of expanding, high assembling accuracy is not required, and assembling operation into the hosing can be easily carried out.